Fighting is raging in the eastern Ukrainian city of Donetsk, one day after pro-Russian rebels there said they were ready to agree to a cease-fire in order to prevent a “humanitarian catastrophe.”

One person was killed and 10 injured in shelling that started early Sunday morning and continued into the day, city council spokesman Maxim Rovinsky told the Associated Press by phone.

Associated Press reporters heard 25 loud explosions in 30 minutes in the center of Donetsk on Sunday. At least 300,000 of the city’s 1 million residents have fled as violence escalates between Ukrainian government forces and pro-Russian separatists.

On Saturday, rebel leader Aleksandr Zakharchenko called for a cease-fire, in a move that could be aimed at increasing international pressure on Ukraine to allow in a Russian aid mission.